A Copper-Rich Multinary Iodido Bismuthate with Cationic Ligands and Broad Red Emission

Lead halide perovskites and related hybrid metal halides exhibit exceptional semiconductor properties, enabling diverse applications in photovoltaics, solid-state lighting, and photocatalysis. Multinary halido metalates, combining multiple metals, offer unique opportunities to tune the optical and electronic properties of these materials for specific applications. Here, we present the synthesis and characterization of (Hpiz)₄BiCu₄I₁₁·2MeCN (piz = piperazine), the most copper-rich molecular iodido bismuthate reported to date, featuring a Cu/Bi ratio of 4:1. It extends the "all-in-one" design concept of halido cuprates with cationic ligands to multinary systems and exhibits a low optical band gap of 1.82 eV (681 nm) and broad red photoluminescence centered at 1.69 eV (735 nm), making it a promising candidate for light-harvesting and near-infrared emission applications. Quantum chemical analyses attribute the reduced band gap to strong electronic interactions between Cu-(I) and Bi-(III). Additionally, the monometallic analogs (H₂piz)-CuI₃ and (H₂piz)-Bi₂I₈ reveal the role of heterometallic interactions in modulating the optical properties. This study provides valuable insights into the design of copper-bismuth iodide systems, enriching the library of hybrid materials with customized semiconductor characteristics.